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BrianX128

KT17 power loss / runs rough at low rpm

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BrianX128

The series 2 kt17 in my new to me 417a had ran great all fall, I got a rpm gauge that operates of the alternator pulses and hooked it up today and noticed it was running rough. Took the gauge off but no difference.

 

It still revs up to wide open throttle [showing 3k rpms on this gauge] and sounds normal there but if I turn the mower deck on or put the engine under load it drops to 2k and sounds like its dying. 

 

I can almost feel something pulsing when the deck is on from the engine going through the rest of the engine. It's running on both cylinders at least from a has spark perspective but barely stays running if I pull one plug on either side.

 

I have no idea what's going on. I thought I lost a flywheel magnet but it's still charging and I know it was balanced fine I mowed with it several times after I re glued my magnets. I'm hoping my usual run of horrible luck didn't strike but my gut tells me something is loose inside in an "I'm not fixing this engine" type of way.

Edited by BrianX128

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pfrederi

or she is starved for fuel.  Carb been cleaned lately???

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520HC

Pull your plugs and check for compression. Don't like to scare you but sounds like running on one cylinder. 

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lynnmor
13 minutes ago, 520HC said:

Pull your plugs and check for compression. Don't like to scare you but sounds like running on one cylinder. 

Yep, it should be 90 psi or more, see page 13.

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BrianX128

Pulling either plug wire will kill it not just one but it will try to hang on for a bit on either so doesn't that basically rule that out? 

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BrianX128

I'm going to run a compression test tonight when I get home, assuming that is good what would be the next thing you guys would suggest I check, the coil / ignition system or the carb?

 

It seems like it's getting enough fuel, but it has ran progressively better since I started using non ethanol gas so maybe it is running so poorly from dirt getting stirred up since I bought it. It just seems odd that it ran perfectly until I let it sit for two weeks of no use and it got way colder outside and now it's annoyed. 

 

I did wash it before I put it away for winter, but I didn't really wash anything near the ignition or engine area and it ran fine back to the upstairs garage that evening.

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pfrederi

When you try to run it on one cylinder then the other does it run about equally on each one.  I know it won't run really well but if it runs about the same no matter which cylinder you are using then I go back to my original comment she is starving for gas.  very weak fuel pump, plugged fuel filter, or dirt in the carb

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BrianX128

It just does the same 10 second "try and keep it together" until it falls on it's face.

 

When I had it wide open the other night when it first started doing this with the mower deck on, I would get a random "cough" out of the exaust. When we first got the mower, you had to run it with the choke pulled 3/4 of the way out to you, now once it's hot you don't need it at all. I figured the carb would be a winter project, but it ran great when you had it at the sweet spot. It almost feels like the engine got out of time or something, there's no audible noise to the "wobble" and it gets better with rpm until the engine is under a load, but if you put your hand on the flywheel cover or anywhere on the engine you don't "feel" a knock or anything, you feel it more from the pto output going through the frame of the entire mower.

 

I'll try and get a video of it running tonight after I do a compression test if I can find my tester. 

 

I have an 18hp briggs 2 cylinder, and I've had a spark plug wire issue with it and when it goes to 1 cylinder the engine sounds very different, but this doesn't seem like that. It almost seems like when I got the old VAC running again after 10 years and I didn't know which way the choke was and adjusted the carb for it to run with the choke on not off, the vibration will "miss" certain rpm bands if you rev it up and down.

Edited by BrianX128

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pfrederi

That it runs equally on one cylinder argues against a compression issue.  Possible of course but unlikely you would have a stick valve or bad rings suddenly on both cylinders.

 

Does using the choke now help hurt or have no effect???

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BrianX128

Hurts now used to help it.

 

I just popped the plugs out, both of them will give me a healthy zap. I don't know where my spark plug tester is, and wanted a little more than the eye test. I'm awake now.

 

Both holes blow a solid whoosh of air out, I can't find my compression tester but I'm looking. Front plug looked wet, back plug looked dry as a bone.. 

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BrianX128

Just found a compression tester, front cylinder is 85 (the one that was wet) and the rear cylinder is 75.

 

I know they aren't the same, but you would think I'd still be running on both. I swear it sounds like I am until the engine is under load.

 

*edit*

 

I might be an idiot. Front plug wasn't sparking, tried swapping plugs and problem follows the wet plug. I don't know if I have another plug to see if it runs normally or not but this is what was in it..

 

ss.jpg.09124e00a213ca1f4673bf565abf366e.jpg

 

I'm hoping it died because the good plug was in the hole with lower compression and that's all that was running it so it didn't matter which plug I pulled it just coasted to a stop.

Edited by BrianX128

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oldlineman

I would try some SeaFome has done wonders for me!

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BrianX128

Yikes.

 

Rookie mistake for sure, that spark plug is bad and that was the only issue. I've never had the "simple thing" be the cause of something like this in my last 100 tries, I guess I was due for one.

 

I don't have whatever that "autolite 25" spark plug is, I just tossed in a random plug from the drawer of old mystery plugs and it fired off and runs normal. Is there a recommended plug for this engine? If so I should probably get two new ones before the other one dies while my wife mows next year on one cylinder.

 

Smoking a lot, but there's a lot of unburnt fuel in that hole I guess. 

 

It's amazing how your mind can trick you into thinking you hear a noise and the engine is running normally when that's far from the truth.

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gwest_ca

Champion plug RV15YC gapped to .025".

Garry

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pfrederi

Autolite 25

 

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BrianX128

 

I have it running with a random plug. I'll get two new good plugs and make sure the points and everything look good tomorrow before I put that behind me.

 

I'm curious if anyone thinks this thing is set to idle too fast or if this gauge seems off just a little. It's a rpm gauge that goes by the poles of the stator from the ac signal. I may not have it at the right setting but the directions were non existent. 

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pfrederi

The ignition on a KT 17 fires both plugs at the same time.  One is on compression and ignites the fuel mix.  The other is firing at the end of the exhaust stoke. (wasted spark)  i think that may be causing a problem with your RPM gauge engine sounds like it is running slower than the rpm indicated especially when you idled it down. I would pick up a cheap hand held tach to set top end and idle is much too slow.

 

 

 

 

Capture.JPG

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BrianX128
1 hour ago, pfrederi said:

The ignition on a KT 17 fires both plugs at the same time.  One is on compression and ignites the fuel mix.  The other is firing at the end of the exhaust stoke. (wasted spark)  i think that may be causing a problem with your RPM gauge engine sounds like it is running slower than the rpm indicated especially when you idled it down. I would pick up a cheap hand held tach to set top end and idle is much too slow.

 

 

 

 

Capture.JPG

 

Thing is this tach runs off pulses from the magnets at the stator it doesn't work off the coil at all .

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pfrederi

Interesting have not heard of a tach that runs off counting the charging stator pulses.  At the 2:06 point you idle it way down, tack was still showing over 1000 sure didn't sound like it.

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BrianX128

So I found the directions, it has pulse settings for 8, 12, and 16 pulses from the stator.

 

This thing has 6 magnets with 3 poles.. which would be 18. I'm not sure what constitutes a "pulse" though. I might try the 16 pulse and see if it's closer, I'm also not sure if the pulses would be determined from the magnets or from the stator poles both end up being 18, but maybe that only makes 9 "pulses" the directions don't make sense there.

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pfrederi
6 hours ago, BrianX128 said:

So I found the directions, it has pulse settings for 8, 12, and 16 pulses from the stator.

 

This thing has 6 magnets with 3 poles.. which would be 18. I'm not sure what constitutes a "pulse" though. I might try the 16 pulse and see if it's closer, I'm also not sure if the pulses would be determined from the magnets or from the stator poles both end up being 18, but maybe that only makes 9 "pulses" the directions don't make sense there.

Way to complex for me...:P  i wasn't very good at geometry/math.

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BrianX128

 

I think this is more accurate now. Idles at 1600 and governs out at 3300. This is with the new p plugs after I filed the points and I cleaned the carb but it wasn't really dirty. 

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Rfp55

Valve clearance and points setting important.  Low compression is most apparent at low rpm, less leakage occurs at high rpm. Good luck with getting through it, just trying and persistence often rewards the fixer. Keep after it. Had one run half good but fail ( lose rpm) under load on snowblower, was just ignition points not set good/burned.

Edited by Rfp55
Mistaken statement,me

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